A promising strontium and cobalt-free Ba1-xCaxFeO3-δ air electrode for reversible protonic ceramic cells

The air electrode with strontium and cobalt elements has the elemental diffusion or delamination issue on the air electrode/electrolyte interface in reversible protonic ceramic cells (RPCCs). Hence the development of strontium and cobalt-free triple conducting (H+/O2-/e-) air electrodes with high electrochemical activity and stability is urgent. Here, we report a strontium and cobalt-free Ba0.8Ca0.2FeO3-δ (BCF82) air electrode with high catalytic activity and electrochemical stability for oxygen reduction/evolution reactions. A RPCC with the BCF82 air electrode shows a high peak power density of 1.14 W cm-2 in the fuel cell mode and a current density of 3.49 A cm-2 under 1.3 V in the electrolysis mode at 700 °C. Furthermore, the cell demonstrates suitable stability in the fuel cell, electrolysis and reversible modes at 600 °C for hundreds of hours without elemental segregation and delamination issue. This work offers an efficient approach to develop low-cost and durable air electrodes for RPCCs.